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Old 05-04-2005, 12:33 PM   #1
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Glueing spar to coroplast

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Any help will be greatly appreciated.

I'm building my first wing and can't seem to get the spar to glue to the wing. I have flashed the area and the spar is mad from clear pine. The flashing is done on the trailing edge as well and no problems getting glue to work there. I'm using medium CA.

Is it possible to use other glue types?
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Old 05-04-2005, 01:04 PM   #2
Wayne MIller
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Glueing Spar


I use mostely Elmers Ployurethane ProBond Glue (note, there is two elmers glue called ProBond - make sure you get the Polyurethane) for doing my SPADs.

This glue requires a small amount of water to set.

I first rough up the area of the Coroplast really well with very rough sandpaper so its kind of fuzzy, this gives a good gripping surface for the glue. I then dampen the area lightly with water using a mist from a spray bottle. I then apply a light coating of polyurethane glue, then give the glue and other surface a light misting of water, then clamp together. It will take a while to set, the instructions say 1 to 4 hours depending on conditions.

The polyurethane glue will expand like crazy for the first 2 hours and then seems to stop. Make sure you put scrap pape or plastic under any area that you think the glue will spill on to. I use wax paper.

I wipe excess of after 1 hour and then again at 2 hours.

If I'm worried about the surrounding areas getting glue on it, I mask off with masking tape. The glue is very difficult to get off once it is set, and will never come out of clothes, so be careful!

I get my glue at Home Depot or Rona, it is expensive, but goes a long ways.

Judging how much expansion that takes place is difficult, to test, just run a bead on a piece of scrap with a mist of water on the scrap, then mist the glue - come back in 2 hours.

You may want to test glueing two pieces of scrap coro, or wood and coro together first to get an idea of how it works.

Hope this helps.


Wayne Miller
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Old 05-04-2005, 01:41 PM   #3
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Possibly you are using too much CA? 1 drop every 1//4" or so is all you need. I have glued many spars to coroplast using medium CA and have always had VERY strong bonds. The only time I had a problem was with the first spar I tried to glue. I used a continuous bead of CA and it wouldn't set worth a darn. Of course make sure both surfaces are clean and oil free. I assume you cleaned the coro with alcohol or glass cleaner to remove the surface oil. A light sanding on the coro doesn't hurt either.

Or as mentioned above try Probond polyurethane glue. It's slower to use but just about foolproof and will give you absolutely bombproof joints!
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Old 05-04-2005, 10:34 PM   #4
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my method:

1)with thinners and a cloth, rub the bejeebers out of the area to be glued (rub till you hand/cloth gets hot).

2)sand with rough sand paper

3) flash it

4) woodpecker it

5) ca it in drops about 1/4" apart and clamp

6) pop it open

7) woodpecker it again

8 ) polyurethane glue one side--in a nice long continuous S-line (like a snake), mist other side lightly with water and clamp

9) NOW do the same procedure to seal the trailing edge.

Works every time for me BUT coro from different regions glues differently (better/worse) as well as different colours glue better/worse.

Experiment with what works for you. Go to my site and download the "gluing" document. A summary of all the gluing tips from the old SPAD site.
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Old 05-05-2005, 06:35 AM   #5
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Never been a problem doing spars?

*Important you use a Flame to burn off the manufacturing oils off the plastic. I use a BBQ or Candle Butane wand and run the flame up/down the area that must be glued. In Spadtothebone this is known as Flaming.

Step 2 Use tiny drops of CA - sort of like doing Rivits and you get 1 go at putting it in place correctly.

Another reason if your using yardsticks is the varnish finish on the wood. Sand off the varnish and the Ca will work better.
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Old 05-05-2005, 08:35 AM   #6
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Can epoxy work if I sand the coro first?

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Old 05-05-2005, 11:25 AM   #7
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Never Tried Epoxy?

I use Ca+ thick stuff - The Ca welds the Coro to the wood or Coro on Coro - The coro will rip before the glue joint fails. Thats strong!!!!

Epoxy won't weld as glue joint and I feel cold weather or hot weather would effect the bond.
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Old 05-05-2005, 09:26 PM   #8
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I've always used probond. Never had a problem. I find if you poke a number of small pinholes along the joint, the probond will expand into these holes during the curing process. A sort of glue rivet. Good luck, it looks like you've been given alot of great advice.
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Old 05-06-2005, 12:21 PM   #9
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Spar to Coro Glue

Ditto on the above. I have used the Poly and CA very effectively. Also have experimented with others and have found the following to be very effective for the spar to coro and all other coro to coro applications.

Lepage Contact Cement 250 ml size

- ease in surface preparation(medium sand the coro only)
- easy to apply-applicator provided
- apply to both surfaces, coro-coro or coro-wood, and let dry 5-10 minutes
- immediate and very strong bond with NO clamping necessary
- it's cheap and available at C Tire and most hardware stores
- on to next segment of build
Have built several SRADS using this contact cement including Kraut's big Ultra SpadStick. Because it is a contact cement once you press the surfaces together that's it, so make sure all is lined up.It's just great IMHO and very suitable if used carefully.
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